Antarctic Freshwater Research Articles

Using Captain Scott's Discovery specimens to unlock the past: has Antarctic cyanobacterial diversity changed over the last 100 years?

Evidence of climate-driven environmental change is increasing in Antarctica, and with it comes concern that this will propagate to impacts on biological communities. Recognition and prediction of change needs to incorporate the extent and timescales over which communities vary under extant conditions. However, few observations of Antarctic microbial communities, which dominate inland habitats, allow this. We therefore carried out the first molecular comparison of Cyanobacteria in historic herbarium microbial mats from freshwater ecosystems on Ross Island and the McMurdo Ice Shelf, collected by Captain R.F. Scott's 'Discovery' Expedition (1902-1903), with modern samples from those areas. Using 16S rRNA gene surveys, we found that modern and historic cyanobacteria assemblages showed some variation in community structure but were dominated by the same genotypes. Modern communities had a higher richness, including genotypes not found in historic samples, but they had the highest similarity to other cyanobacteria sequences from Antarctica. The results imply slow cyanobacterial 16S rRNA gene genotype turnover and considerable community stability within Antarctic microbial mats. We suggest that this relates to Antarctic freshwater 'organisms requiring a capacity to withstand diverse stresses, and that this could also provide a degree of resistance and resilience to future climatic-driven environmental change in Antarctica.

Transcriptome sequencing of an Antarctic microalga, Chlorella sp. (Trebouxiophyceae, Chlorophyta) subjected to short-term ultraviolet radiation stress

Stratospheric ozone depletion has led to increasing levels of ultraviolet radiation (UVR) reaching the Earth’s surface. Elevated UVR, particularly in the high latitudes, potentially causes shifts in species composition and diversity in various ecosystems, consequently altering the biogeochemical cycles. Microalgae are not only ecologically important as primary producers, generating atmospheric oxygen and sequestering carbon dioxide; they are also economically important as sources of health supplement, pigments, biofuel and others. Changes to the size and composition of algal communities can lead to profound impacts to the fisheries productivity. There have been studies on the effects of UVR on the growth, photosynthesis and biochemical composition of microalgae, but limited information on the underlying molecular mechanisms involved in the response and adaptation of microalgae to UVR is available. We employed RNA-seq to quantitatively evaluate and compare the transcriptomes of an Antarctic freshwater Chlorella sp. grown at ambient versus elevated UVR conditions. Differentially expressed genes, relating to the fatty acid degradation, amino acid metabolism, starch and sucrose metabolism and peroxisome pathways, suggest conservation and remobilisation of energy resources, maintenance of newly synthesised protein and inhibition of protein degradation, ensuring membrane lipid homeostasis and regulating antioxidative mechanisms, as the acclimation strategies in response to UVR. These findings expand current knowledge of gene expression in polar Chlorella sp. in response to short-term UVR. Studies on stress tolerance mechanisms are important to understand and predict future impacts of climate change. Genes, proteins and pathways identified from these adaptable polar algae have potentially far-reaching biotechnological applications.

Draft Genome Sequence of the Axenic Strain Phormidesmispriestleyi ULC007, a Cyanobacterium Isolated from Lake Bruehwiler (Larsemann Hills, Antarctica).

ABSTRACTPhormidesmis priestleyi ULC007 is an Antarctic freshwater cyanobacterium. Its draft genome is 5,684,389 bp long. It contains a total of 5,604 protein-encoding genes, of which 22.2% have no clear homologues in known genomes. To date, this draft genome is the first one ever determined for an axenic cyanobacterium from Antarctica.

Bioactivities of ethanol extract from the Antarctic freshwater microalga, Chloromonas sp.

Cancer is the principal cause of human death and occurs through highly complex processes that involve the multiple coordinated mechanisms of tumorigenesis. A number of studies have indicated that the microalgae extracts showed anticancer activity in a variety of human cancer cells and can provide a new insight in the development of novel anti-cancer therapy. Here, in order to investigate molecular mechanisms of anticancer activity in the Antarctic freshwater microalga, Chloromonas sp., we prepared ethanol extract of Chloromonas sp. (ETCH) and performed several in vitro assays using human normal keratinocyte (HaCaT) and different types of cancer cells including cervical, melanoma, and breast cancer cells (HeLa, A375 and Hs578T, respectively). We revealed that ETCH had the antioxidant capacity, and caused significant cell growth inhibition and apoptosis of cancer cells in a dose-dependent manner, whereas it showed no anti-proliferation to normal cells. In addition, ETCH had a significant inhibitory effect on cell invasion without the cytotoxic effect. Furthermore, ETCH-induced apoptosis was mediated by increase in pro-apoptotic proteins including cleaved caspase-3 and p53, and by decrease in anti-apoptotic protein, Bcl-2 in ETCH-treated cancer cells. Taken together, this work firstly explored the antioxidant and anticancer activities of an Antarctic freshwater microalga, and ETCH could be a potential therapeutic candidate in the treatment of human cancer.

Two new Gomphonema species (Bacillariophyta) from the Maritime Antarctic Region

Two new diatom taxa belonging to the genus Gomphonema were recorded during a survey of the Maritime Antarctic freshwater and limno-terrestrial diatom flora: Gomphonema jamesrossense sp. nov. and G.maritimo-antarcticum sp. nov. Detailed light (LM) and scanning electron microscope (SEM) observations are used to characterize the morphology and ultrastructure of the two new Gomphonema taxa. Comparisons with similar taxa and the ecological preferences of each species are added. The revision of these species confirmed the endemic nature of the Antarctic diatom flora.

New Cysteine-Rich Ice-Binding Protein Secreted from Antarctic Microalga, Chloromonas sp.

Many microorganisms in Antarctica survive in the cold environment there by producing ice-binding proteins (IBPs) to control the growth of ice around them. An IBP from the Antarctic freshwater microalga, Chloromonas sp., was identified and characterized. The length of the Chloromonas sp. IBP (ChloroIBP) gene was 3.2 kb with 12 exons, and the molecular weight of the protein deduced from the ChloroIBP cDNA was 34.0 kDa. Expression of the ChloroIBP gene was up- and down-regulated by freezing and warming conditions, respectively. Western blot analysis revealed that native ChloroIBP was secreted into the culture medium. This protein has fifteen cysteines and is extensively disulfide bonded as shown by in-gel mobility shifts between oxidizing and reducing conditions. The open-reading frame of ChloroIBP was cloned and over-expressed in Escherichia coli to investigate the IBP’s biochemical characteristics. Recombinant ChloroIBP produced as a fusion protein with thioredoxin was purified by affinity chromatography and formed single ice crystals of a dendritic shape with a thermal hysteresis activity of 0.4±0.02°C at a concentration of 5 mg/ml. In silico structural modeling indicated that the three-dimensional structure of ChloroIBP was that of a right-handed β-helix. Site-directed mutagenesis of ChloroIBP showed that a conserved region of six parallel T-X-T motifs on the β-2 face was the ice-binding region, as predicted from the model. In addition to disulfide bonding, hydrophobic interactions between inward-pointing residues on the β-1 and β-2 faces, in the region of ice-binding motifs, were crucial to maintaining the structural conformation of ice-binding site and the ice-binding activity of ChloroIBP.

An Early Permian, paleopolar, postglacial, river-dominated deltaic succession in the Mackellar–Fairchild formations at Turnabout Ridge, Central Transantarctic Mountains, Antarctica

Turnabout Ridge, a remote outcrop belt in the Beardmore Glacier Region of the Central Transantarctic Mountains, comprises subglacial–glaciomarine deposits of the Pagoda Formation (Fm) overlain by a postglacial deltaic succession of the Mackellar–Fairchild formations (fms). Four depositional environments were identified in the Mackellar–Fairchild fms: 1) prodelta to distal-delta-front deposits that record the initial filling of a newly formed intracratonic basin; 2) an interval dominated by subaqueous terminal distributary channels and levees that signal the advancement of a delta into the region; 3) mouth bars and associated subaqueous terminal distributaries representing the proximal delta front; and 4) an overlying sand-dominated braidplain.A companion ichnologic study identified 30 ichnogenera in the Mackellar Fm that combine to form six ichnocoenoses. Twelve traces are known only from marine settings, 18 are found across marine, brackish, and freshwater systems, and none are known solely from freshwater systems. The ichnology refines paleoenvironmental and paleosalinity interpretations for the Mackellar Fm, and indicates a predominantly brackish water paleoenvironment.Subaqueous terminal distributary channels record the highest energies, suspended sediment concentrations, and sediment loads, and are the conduits that delivered sediment to the delta front and prodelta. Abundant traction deposits (hyperpycnites) displaying only minor wave or tide modification suggest that the delta is best classified as river-flood dominated. The succession exhibits similarities to the Panther Tongue and Ferron Notom deltas of the Cretaceous Western Interior Seaway, USA, and a Late Ordovician proglacial delta from the Murzuq Basin in Libya.The combined ichnologic and sedimentologic evidence suggests that sediment-laden glacial outburst floods produced freshets that recurrently prepped a shallow-marine basin, reducing salinities and allowing for abundant channelization and hyperpycnite deposition along the delta front. Turnabout Ridge likely occupied a proximal and axial position relative to an Antarctic freshwater- and sedimentation-stressed, river-dominated marine deltaic system along the shoreline of an epeiric seaway during the Early Permian.

Three new Craticula species (Bacillariophyta) from the Maritime Antarctic Region

Three new diatom taxa belonging to the genus Craticula were found during the ongoing taxonomic revision of the Antarctic freshwater and limno-terrestrial diatom flora: Craticula australis, sp. nov., C. obaesa, sp. nov and C. petradeblockiana, sp. nov. Detailed light and scanning electron microscope observations are used to better characterize the morphology and ultrastructure of these three new taxa. A fourth Craticula taxon, formerly identified as Navicula megacuspidata, described from South Georgia, is transferred to the genus Craticula and its taxonomy is briefly discussed. Comparisons with similar taxa and the ecological preferences of each species are added. The revision of these species confirms once again the endemic nature of the Antarctic diatom flora.

The effect of increased fresh water from Antarctic ice shelves on future trends in Antarctic sea ice

AbstractObservations show that, in contrast to the Arctic, the area of Antarctic sea ice has increased since 1979. A potential driver of this significant increase relates to the mass loss of the Antarctic ice sheet. Subsurface ocean warming causes basal ice-shelf melt, freshening the surface waters around Antarctica, which leads to increases in sea-ice cover. With climate warming ongoing, future mass-loss rates are projected to accelerate, which has the potential to affect future Antarctic sea-ice trends. Here we investigate to what extent future sea-ice trends are influenced by projected increases in Antarctic freshwater flux due to subsurface melt, using a state-of-the-art global climate model (EC-Earth) in standardized Climate Model Intercomparison Project phase 5 (CMIP5) climate-change simulations. Virtually all CMIP5 models disregard ocean–ice-sheet interactions and project strongly retreating Antarctic sea ice. Applying various freshwater flux scenarios, we find that the additional fresh water significantly offsets the decline in sea-ice area and is even able to reverse the trend in the strongest freshwater forcing scenario that can reasonably be expected, especially in austral winter. The model also simulates decreasing sea surface temperatures (SSTs), with the SST trends exhibiting strong regional variations that largely correspond to regional sea-ice trends.

The diversity of bacteria isolated from antarctic freshwater reservoirs possessing the ability to produce polyhydroxyalkanoates.

The diversity of polyhydroxyalkanoates-producing bacteria in freshwater reservoirs in the Ecology Glacier foreland, Antarctica, was examined by a cultivation-dependent method. Isolated strains were analyzed phylogenetically by 16S rRNA gene sequencing, and classified as members of Alpha-, Beta-, or Gammaproteobacteria classes. Polymerase chain reaction was used to detect PHA synthase genes. Potential polyhydroxyalkanoates (PHAs) producers belonging mainly to Pseudomonas sp., and Janthinobacterium sp. were isolated from all five sampling sites, suggesting that PHA synthesis is a common bacterial feature at pioneer sites. All Pseudomonas strains had the genetic potential to synthesize medium-chain-length PHAs, whereas some isolated Janthinobacterium strains might produce short-chain-length PHAs or medium-chain-length PHAs. It is the first report revealing that Janthinobacterium species could have the potential to produce medium-chain-length PHAs.

Four Achnanthidium species (Bacillariophyta) formerly identified as Achnanthidium minutissimum from the Antarctic Region

Four taxa belonging to the complex of species around Achnanthidium minutissimum were found during the ongoing taxonomic revision of the Antarctic freshwater and limno-terrestrial diatom flora. Two taxa were previously described as Achnanthidium lailae and A. sieminskae. Two others were formerly identified as A. minutissimum but detailed light and scanning electron microscopical observations revealed sufficient morphological differences compared to the type of A. minutissimum, to justify their separation and description as new taxa: Achnanthidium indistinctum and A. maritimo-antarcticum. The morphology and ecology of all four taxa are discussed comparing the species with morphologically similar taxa. The biogeographical consequences of the splitting of the former A. minutissimum complex in the Antarctic Region are discussed.

Nitrate and ammonium ions contents in field minibioreactors with Antarctic freshwater autotrophs

The content of nitrate and ammonium ions in aquatic environment is an important factor in the development of microorganisms colonies especially in low-nutrient environment. In this study, field experiments using small-volume minibioreactors were performed directly on the James Ross Island in Antarctica in order to describe changes in nitrate and ammonium ions contents in the Antarctic environment The ion concentrations in minibioreactors with local freshwater autotrophs was monitored for increased eutro-phication conditions. The content of nitrogen forms was determined in water samples taken from the minibioreactors regularly. Samples were taken to the laboratory of the Johann Gregor Mendel station where nitrogen content was evaluated using ion-selective electrodes. Furthermore, the freshwater autotrophs was subjected to basic taxonomic study. Closed system of the minibioreactors allowed the monitoring of nitrogen speciation changes which take place in the environment. These changes can be attributed to both the biological activity of microorganisms and external conditions. Increased eutrophication of water did not induce a rapid development of the freshwater autotrophs.

Using data assimilation to investigate the causes of Southern Hemisphere high latitude cooling from 10 to 8 ka BP

Abstract. From 10 to 8 ka BP (thousand years before present), paleoclimate records show an atmospheric and oceanic cooling in the high latitudes of the Southern Hemisphere. During this interval, temperatures estimated from proxy data decrease by 0.8 °C over Antarctica and 1.2 °C over the Southern Ocean. In order to study the causes of this cooling, simulations covering the early Holocene have been performed with the climate model of intermediate complexity LOVECLIM constrained to follow the signal recorded in climate proxies using a data assimilation method based on a particle filtering approach. The selected proxies represent oceanic and atmospheric surface temperature in the Southern Hemisphere derived from terrestrial, marine and glaciological records. Two mechanisms previously suggested to explain the 10–8 ka BP cooling pattern are investigated using the data assimilation approach in our model. The first hypothesis is a change in atmospheric circulation, and the second one is a cooling of the sea surface temperature in the Southern Ocean, driven in our experimental setup by the impact of an increased West Antarctic melting rate on ocean circulation. For the atmosphere hypothesis, the climate state obtained by data assimilation produces a modification of the meridional atmospheric circulation leading to a 0.5 °C Antarctic cooling from 10 to 8 ka BP compared to the simulation without data assimilation, without congruent cooling of the atmospheric and sea surface temperature in the Southern Ocean. For the ocean hypothesis, the increased West Antarctic freshwater flux constrainted by data assimilation (+100 mSv from 10 to 8 ka BP) leads to an oceanic cooling of 0.7 °C and a strengthening of Southern Hemisphere westerlies (+6%). Thus, according to our experiments, the observed cooling in Antarctic and the Southern Ocean proxy records can only be reconciled with the reconstructions by the combination of a modified atmospheric circulation and an enhanced freshwater flux.

Lysobacter oligotrophicus sp. nov., isolated from an Antarctic freshwater lake in Antarctica

A Gram-stain-negative, non-spore-forming, rod-shaped, aerobic bacterium (strain 107-E2(T)) was isolated from freshwater samples containing microbial mats collected at a lake in Skarvsnes, Antarctica (temporary lake name, Lake Tanago Ike). Strain 107-E2(T) grew between 5 and 25 °C, with an optimum of 23 °C. Moreover, colony formation was observed on agar media even at -5 °C. The pH range for growth was between 6.0 and 9.0, with an optimum of pH 7.0-8.0. The range of NaCl concentration for growth was between 0.0 and 0.5% (w/v), with an optimum of 0.0%. No growth was observed in media containing organic compounds at high concentrations, which indicated that strain 107-E2(T) was an oligotroph. In the late stationary phase, strain 107-E2(T) produced a dark brown water-soluble pigment. Esterase, amylase and protease production was observed. Antimicrobial-lytic activities for Gram-negative bacteria and yeast were observed. Ubiquinone-8 was the major respiratory quinone. The major fatty acids were iso-C15:0, iso-C(17:1)ω9c and iso-C(15:1) at 5. The G+C content of genomic DNA was 66.1 mol%. Analysis of the 16S rRNA gene sequences revealed that strain 107-E2(T) belonged to the genus Lysobacter, and low DNA-DNA relatedness values with closely related species distinguished strain 107-E2(T) from recognized species of the genus Lysobacter. The phylogenetic situation and physiological characteristics indicated that strain 107-E2(T) should be classified as a representative of a novel species of the genus Lysobacter, for which the name Lysobacter oligotrophicus sp. nov. is proposed. The type strain is 107-E2(T) ( =JCM 18257(T) =ATCC BAA-2438(T)).

Bacterial diversity of the rock-water interface in an East Antarctic freshwater ecosystem, Lake Tawani(P)†

Schirmacher Oasis is one of the few ice-free plateaus in East Antarctica that maintains a unique distribution of over 120 microbial-rich, dynamic freshwater lakes, most of which are unexplored. In this study, we describe the bacterial diversity of the rock-water interface in Lake Tawani(P) using culture-independent Bacterial Tag Encoded FLX Amplicon Pyrosequencing (bTEFAP), clone library construction, and culture-based analysis targeting the eubacterial 16S rRNA gene. Lake Tawani(P)was formed in a fossil valley by the accumulation of snow and glacial melt through surface channels into a low-catchment depression. Overall this lake exhibited thirteen bacterial phyla and one-hundred and twelve genera. The Qiime bioinformatics analysis on the bTEFAP alone exhibited higher coverage of the bacterial composition in Lake Tawani(P) than the clone library construction or culture-based methodology. Particularly due to the higher sensitivity of the bTEFAP approach, we detected and differentiated members of the phyla: Chloroflexi, Gemmatimonadetes, Planctomycetes, Nitrospira, and Candidate Division TM7 that other methods were unable to reveal. Nevertheless we found that the use of multiple approaches identified a more complete bacterial community than by using any single approach. Investigating the bacterial diversity of the Schirmacher Oasis lakes, especially those connected through surface channels and encompassed by valleys, will help unravel the dynamic nature of these unique seasonal, freshwater lakes, which potentially harbors highly adapted bacterial taxa with defined ecological functions.

The freshwater balance of polar regions in transient simulations from 1500 to 2100 AD using a comprehensive coupled climate model

The ocean and sea ice in both polar regions are important reservoirs of freshwater within the climate system. While the response of these reservoirs to future climate change has been studied intensively, the sensitivity of the polar freshwater balance to natural forcing variations during preindustrial times has received less attention. Using an ensemble of transient simulations from 1500 to 2100 AD we put present-day and future states of the polar freshwater balance in the context of low frequency variability of the past five centuries. This is done by focusing on different multi-decadal periods of characteristic external forcing. In the Arctic, freshwater is shifted from the ocean to sea ice during the Maunder Minimum while the total amount of freshwater within the Arctic domain remains unchanged. In contrast, the subsequent Dalton Minimum does not leave an imprint on the slow-reacting reservoirs of the ocean and sea ice, but triggers a drop in the import of freshwater through the atmosphere. During the twentieth and twenty-first century the build-up of freshwater in the Arctic Ocean leads to a strengthening of the liquid export. The Arctic freshwater balance is shifted towards being a large source of freshwater to the North Atlantic ocean. The Antarctic freshwater cycle, on the other hand, appears to be insensitive to preindustrial variations in external forcing. In line with the rising temperature during the industrial era the freshwater budget becomes increasingly unbalanced and strengthens the high latitude’s Southern Ocean as a source of liquid freshwater to lower latitude oceans.

Temperature effects on carbon and nitrogen metabolism in some Maritime Antarctic freshwater phototrophic communities

Biofilms growing on ice and benthic mats are among the most conspicuous biological communities in Antarctic landscapes and harbour a high diversity of organisms. These communities are consortia that make important contributions to carbon and nitrogen input in non-marine Antarctic ecosystems. Here, we study the effect of increasing temperatures on the carbon and nitrogen metabolism of two benthic communities on Byers Peninsula (Livingston Island, Maritime Antarctica): a biofilm dominated by green algae growing on seasonal ice, and a land-based microbial mat composed mainly of cyanobacteria. Inorganic carbon photoassimilation, urea and nitrate uptake and N2-fixation (acetylene reduction activity) rates were determined in situ in parallel at five different temperatures (0, 5, 10, 15, 25°C) using thermostatic baths. The results for the cyanobacterial mat showed that photosynthesis and N2-fixation responded positively to increased temperatures, but urea and NO3− uptake rates did not show a significant variation related to temperature. This microbial mat exhibits relatively low activity at 0°C whereas at higher temperatures (up to 15°C), N2-fixation rate increased significantly. Similarly, the maximum photosynthetic activity increased in parallel with temperature and showed no saturation up to 25°C. In contrast, the ice biofilm displayed higher photosynthetic activity at 0°C than at the other temperatures assayed, and it showed elevated photoinhibition at warmer temperatures.

Millennial-scale oscillations in the Southern Ocean in response to atmospheric CO 2 increase

A coupled climate-ice-sheet model is used to investigate the response of climate at the millennial time scale under several global warming long-term scenarios, stabilized at different levels ranging from 2 to 7 times the pre-industrial CO 2 level. The climate response is mainly analyzed in terms of changes in temperature, oceanic circulation, and ice-sheet behaviour. For the 4 × CO 2 scenario, the climate response appears to be highly non-linear: abrupt transitions occur in the Southern Ocean deep water formation strength with a period of about 1200 yr. These millennial oscillations do not occur for both lower and larger CO 2 levels. We show that these transitions are associated with internal oscillations of the Southern Ocean, triggered by the Antarctic freshwater budget. We first analyse the oscillatory mechanism. Secondly, through a series of 420 sensitivity experiments we also explore the range of temperature and freshwater flux for which such oscillations can be triggered.

Rotifers as Indicators of Climate Change in the Antarctic Environments

An important question stated in the presented paper is: Could rotifers be the indicators of climate change in the Antarctic environments? Rotifers are one of the most important components of the invertebrate fauna of the Antarctic freshwater and terrestrial ecosystems. However, investigations of their distribution, diversity and an ecological role in the environment have been widely neglected, mainly due to the methodological and taxonomical difficulties. During the investigations 176 species of rotifers were found, including the endemic and cosmopolitan species. Their existence is directly proportional to microvariations of humidity factor. Scientists still have poor knowledge about the occurrence of rotifer species in recently studied habitats e.g. cryoconite holes, nunataks or soil. Probably rotifers could be the indicators of climate change in the Antarctic freshwater and terrestrial ecosystems but more investigations and monitoring studies are needed

A thermodynamic model of freshwater Antarctic lake ice

Antarctic lakes with simple plankton ecosystems are believed to be sensitive biological indicators of climate change. Models of the physical environment, in particular the ice layer, support understanding of how the ecosystems respond to meteorological variables. This paper describes how data from a previously reported automatic measuring probe and meteorological data from Davis station were used to develop a detailed thermodynamic model of the ice layer on Crooked Lake, one of the largest and deepest freshwater lakes in Antarctica. The general model structure is similar to a previously reported model of sea ice but with modifications specific to the Antarctic freshwater lake case informed by the data. The model inputs are atmospheric variables as well as water temperature, ice albedo and the radiation extinction coefficient for the ice. Heat and radiation fluxes at the ice–air and ice–water boundaries are calculated using equations chosen for their suitability for the Antarctic. In the case of shortwave radiation, equations were fitted to data from the automatic probe. Using the heat fluxes to establish boundary conditions, and incorporating the known thermodynamic properties of ice, the temperature profile within the ice and the resulting growth and melt of the ice can be calculated. The model uses a largely mechanistic approach, with most equations taken from established thermodynamic theories or empirical studies and only one adjustable parameter related to the sensible heat flux from the water, which is not easily calculated from the available data. It was found to accurately reproduce ice temperature and ice thickness data for the year 2003, with r 2 = 0.89, n = 2005. Finally, the model was simplified to run with air temperature as the only input variable and was shown to perform well—this suggests that freshwater lake ice is affected more by air temperature than any other variable, and is therefore a useful indicator of climate change in its own right.